This CD contains the page images and searchable text from a 1929 United States Geological Survey report on the gold-bearing formations of the 120-mile-long Mother Lode System of California. Between 1849 and 1924, this Sierra Nevada system of gold deposits yielded over $240 million, half of the production coming from the 10-mile segment between the communities of Plymouth and Jackson. USGS Professional Paper 157 expands upon the early USGS report by F. L. Ransome: Geologic Atlas of the United States, Folio #63 - Mother Lode District Special Folio
(1899), which is also included on this CD.
Knopf notes the variety of gold deposits that occur in the Mother Lode system and expects focus to shift from mining the quartz-filled fissures to exploitation of the other ore bodies. By the 1920s, the quartz mines had reached depths of 4,500 feet from surface elevations of 1,500 to 2,700 feet, and Knopf projects economic mining to depths of 6,000 feet. "Mining on the Mother Lode belt is favored by nearness to supply centers, by good transportation facilities, labor supply, and climatic conditions, and by the slow increase of rock temperature in depth. These advantages are partly offset in the mining of the quartz veins by the moderate gold content of the ore, the moderate size of the ore bodies, and the high cost of timbering, due to heavy ground."
The report investigates the geology traversed by the Mother Lode system, with extensive descriptions and differentiation of the steeply dipping slates, schists, and greenstones, and of the intrusive masses of serpentine. The quartz veins are systems of parallel or acutely intersecting veins, and as many as four have been worked at a single mine. Knopf notes their discontinuous nature, and that few can be traced for more than a few thousand feet. "They cut the inclosing rocks at an acute angle in both strike and dip, and fill fissures that were formed by reverse faulting... Valuable ore bodies have formed in rocks of many kinds. Probably the only valid generalization is the one made by Ransome that paying veins may occur in any rock with the possible exception of serpentine. However, the slate appears to be more favorable than the greenstone, and veins wholly inclosed in greenstone are likely to be of low grade."
This 85-page general discussion of lode geology notes the importance of gold deposits in the wall rocks. It details the mineralogy of the quartz veins and of the adjacent formations. The twelve appended plates include a color geologic map of the Mother Lode belt, photographs of quartz and mineral samples, an isometric diagram of the workings of the Morgan and Melones mines, and profiles and maps of several mines.
See the table of contents for The Mother Lode System of California.
Also included on this CD is Bulletin 141, Geologic Guidebook Along Highway 49-Sierran Gold Belt. This is a 1948 motorists' guide to the gold veins, early history, and historic buildings of the Mother Lode, which is traced by the route of Highway 49. This 166-page publication was compiled by the State of California for the centennial of the Gold Rush. The volume contains a series of geologic maps covering the entire highway, a strip of country 277 miles in length. Numerous photographs and other illustrations accompany the articles on the history of the Gold Rush, the mines, minerals, and rocks of the region, and dozens of Gold Rush structures which had survived to 1948.
See the table of contents for Geologic Guidebook Along Highway 49.